Protective apparatus



May 18 1926.

D. O. WHELAN .PROTECTIVE APPARATUS Filed May 15, 1925 Fig. l:

P/rofc T/ Vf LAMP ,UHT E E mlM Inventor: Dow O.VVhelan, i

b5 Hfs Attorney.

`Patented May 18, 1926.

UNITED STATES PATENT oFFicE,

DOW O. WHELAN, OF SCHIENECTADY, NEW YORK, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

riiofrEcTivE APPARATUS:

l.Application filed May 13, 1925. Serial No. 30,029.

My present invention relates to protective apparatus especially adapted for use in therinionic amplifier systems.

In the operation of thermionic amplifier systems, such for example, as those employed for radio reception, difficultyis' sometimes experienced by the accidental impressing of the B-battery voltage across the filament terminals ofthe thermionic amplifier tubes,

resulting in the burning out of the filaments..

It sometimes happens also that if a short circuit occurs in the socket whereby the full B battery voltage is impressed upon the transformer coils, these coils may be seriouslyv damaged by reason of the heavy current flowing therein. D 'Ihe object of my invention is to provide an apparatus for protecting the amplifying apparatus from both of these dangers. I

It has been proposed to employ in series with the supply batteries of an amplifying set, a resistance of. such value that the maximum current which canlflow undersliortcircuit conditions, or when the full battery volta-ge is applied to the filament terminals will be too small to cause any damage. This, however, requires the use of different values of resistance in case different potentials are used for different devices, and may also produce a harmful reaction between the circuits of the v'different devices.

I have found that it is possible to overcome the disadvantages in the previpusly suggested methods of employing resistances by the use of a resistance which varies 1n` a critical manner with variations in its temperature. Such a resistance may be con- .veniently of the form of a tungsten ilament .enclosed in an atmosphere of hydrogen or other inert gas. The resistance of this lilaF ment at the normaloperating temperature may be comparatively low, but if the current passing through it tends to increase above a certain critical value the resistance will increase very greatly and thus limit the cu r rent to some predetermined value which will not damage the apparatus,at the saine time give a visible indication of the short-circuit condition. 'l I have also found that Ait is possible to construct a single device which will take care of the requirements ofthe situation in the case 'where diierent voltages. are empleoyed for different amplers. This may "accomplished by providing a contactl to some intermediatel point in the filament so chosen that a portion ofthe filament may beconnected in series with the devices :which are supplied with current at a lower potential f while the entire lilament is connected in series with the devices which are supplied with a higher operating potential, the signal thus indicating. inwhich circuit the trouble occurs. j v

The novel features which vI believe to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and method of operation will best be understood by reference to the following description taken in connection wtli .supplying plate potential to the detector tubes; 3 represents a second 45 volt battery,

which may be employed iii series with 2 for supplying volts to certain ampliertubes;

4 represen-ts'another 45 volt battery, which' t, may be connected in series with 2 and 3 for supplying 135 volts to a higher power amplifier' tube; 5 represents a C battery which may be provided with taps as indicated, for furnishing grid bias to the diferent tubes.'

The protective device 6 has a filament 7, enclosed in an evacuated bulb 8, containing 'a filliiig'oiA hydrogen or other nonoXidizing gas. Filament 7 has one terminal connected to the positive terminal of battery 2 and the other terminal to the negative terminal of battery 3 so that the operating current supplied to the amplifier tubesoperating at 90 and 135 volts is required to ow throu hv the entire length of the lament. The ament is ta pecl at an 'intermediatepoint 9- aud from t is tap voltage. may be supplied to the detector tubegs, so that the current to' minal is not shown. ,The whole device may l be constructed in a manner similar to that employed for automobile lamps. The intermediate tap 9 tothe vfilament 7V is also connected to a leading-in conductor extending through the 'stem 1Q, and this leading-in conductor is connected at 13 to the shell 121'- Contact may be made to the.v

of. the base. three terminals'thus provided by meansA of any suitable vform of socket. A

It, will `be seen that by the arrangement described, if a conductor which is connected to the posit-ive terminal of a .plate battery should accidentally come into direct contact with a negative filament terminal, the current which'will thusbe caused to How in the filaments will have to pass through the filament 7 of the protective device. By 4the proper proportion of the filament 7 its re. sistance may be made to increase to such an' extent that the maximum current which will o'wthrongh it at the maximum battery potential which may be applied under these circumstances will be too small to 'burn out the filamentsv of the tubes. The effective limitation of tli"current obtained in this way will also'bsuficient to prevent anyl injury to the transformer windings connecting `successive amplifying. tubes `in case of the direct application of the full battery voltage across a transformer winding. In each case the filament will glowthus giving the danger signal which will allow the batteries to be disconnected before they are damaged.

If desired, a similar protective lamp may` 'be employedat the 'unction between batteries 1 and 2, a portion of the filament being connectedto supply and regulate current to the filaments of the tubes while the en- Atire filament is connected -in series with the B battery. Other modifications of the manner of using the protective device as well as in the precise form of device employed may be.made Without departing from the scope of my invention as set forth in the appended claims.

What I claim as new and desire to secure byLetters Patent of theUnited States, is,-

`1. A protective device for an amplifying system having a plurality of thermionic discharge devices and sources of potential of different 'value for different devices, com-v prising a resistance which varies in value in a critical -manner with thel current` flowing therein, said resistance being so connected .to the system that the operating 'current'supplied from a source of lower potential is required to iow through a portlon only of the resistance, and the operating current supplied from 'a source of higherpotential is re- 'with the current flowing therein, said resistance having one terminal connected to the positive terminal of one of said sources, and

its other terminal connected to the negative terminal of another of saidsources, and a connection to an intermediate point of said resistance for supplying operating current to one 'of said devices at a lower potential than that of other devices.

3. A protective device for an amplifying' system having a plurality' of thermionic discharge devices and sources of potential of different value for supplying di'erent circuits comprising a 'resistance which varies in value in a critical manner withl the current owing therein, said resistance being so connected to the system that the operating current supplied'from one of said sources is required to iiow through a portion only of the resistance and the operating current supplied from another source is required to How through the entire resistanceI`r1 4. A protective device for an amplifying system having a plurality of thermionic dischargedevices and a plurality of sources of potential for supplying different circuits comprising a resistance which varies in value in a critical manner with the current iowing therein, said resistance having one terminal connected to the positive terminal of one of said sources and its othervterminal connected to the negative terminal of ansusl other of said sources, and a connection to an intermediate point of said resistance for supplying operating current to one of the circuits of said system. l

5. A protective device of an amplifying system having a plurality of sources'of potential for supplying different circuits comprising a resistanceso connected to the system that the operating current supplied to one circuit is required to flow through a portion only of the resistance and the operating current supplied to another circuit is re- -quired to flow through theentire resistance,

said resistance' having a comparatively low value when the normal o erating current tiows therethrough, buthavmg the property of increasing greatlyA in value 'when the current iiowingV therethrough jappreciably exceeds .the` normalfcur'rent.

6. A protective device for an electrical network comprisinga plurality of circuits to which dierent potentials are supplied com'- prising a resistance so connected to thel system that the' operating current supplied to one circuit is required to flow through a portion only of the resistance when the operating current supplied to anothercircuit is required to flow through the entire resistance,

said resistance having a comparatively low 'value when the normal -operating current 'flows therethrough and having the'property of increasing greatly in value ,when the eur- I rent flowing therethrough appreciably Aexceeds the normal current.

47. A protective device for an electrical network having a plurality of circuits adapted to be supplied by different potentials comprising a resistance which varies in value in a critical manner with the current flowing thereinLsaid resistance being so connected to the system that the operating current supplied froln a source of lower potential is required to flow through a portion only of the resistance and the operating current supplied from a source of higher potential is required to How through the entire resistance.

vIn witness whereof, I have hereunto set my hand this 11th day of May, 1925.

DOW O. WHELAN. 

